1. Field of the Invention
This invention generally relates to a display apparatus, and more particularly to a fluorescent display apparatus suitable for indicating a frequency in a wireless telegraphic apparatus, a numerical value in measuring instruments or the like.
2. Description of the Prior Arts
In the conventional radio receiver or the like, the frequency received by the radio receiver is indicated by a moving pointer which moves mechanically using a driving mechanism along a dial or scale on which calibrations of frequency are shown.
Recently, with the development and practical use of various display elements, an indicating apparatus, such as, for example, a frequency indicating device explained above, in the form of an electronic device has come into actual use. The electronic indicating device remarkably improves such various deficiencies in the mechanical indicating apparatus such as not being strong enough to withstand external shock, being fragile, requiring more mounting space, and being difficult to read the calibrations at night or in a dark place.
The electronic indicating apparatus includes, as shown in FIG. 1, display elements 1 which may be made of light emitting diodes, anodes having deposited phosphor layers thereon to emit light upon impingement of electrons, or discharge cells which are filled with ionizable gas and emit light by gas discharge. The display elements 1 are linearly or curvedly arranged, and the calibrations 2 which may be made of display elements similar to the elements 1 are provided adjacent to the display elements 1. The display is effected by energizing a predetermined display element among the linearly or curvedly arranged display elements in accordance with an input signal to be displayed.
However, in the conventional display apparatus of this type, it is necessary to extend a number of lead wires corresponding to the number of the display elements 1 out of an envelope of the display apparatus, because the display is effected by selectively energizing one of the display elements related to the input signal. Thus, there must be provided an increased number of lead wires and driving sections for energizing each of the display elements separately, which makes it difficult to effect minute display in the display device and increases the manufacturing costs.
In other words, it is difficult to increase the number of the display elements 1 arranged on the display apparatus in order to enhance the resolution of the display, and also it is difficult to make the display range wide. A static driving system and a dynamic driving system for such a display are known. The static driving system drives the display apparatus by applying a drive signal individually to each of the display elements 1 as explained above. The dynamic driving system effects the display by applying a display signal to the display elements 1 which are divided into consecutive groups with connections between the corresponding positions of each of the groups and by scanning each group of the anodes with pulse signals.
In the dynamic driving system, it is possible to significantly decrease the number of lead wires which come out of the envelope of the display device. However, this system is not acceptable as a driving system of communication appliances or measuring instruments, because the scanning pulses for each group of the anodes create noise in the adjacent communication appliances or measuring instruments and cause the malfunction of these appliances.